I was just pointing out that while nearly everyone knows that the seasons are switched between the hemispheres, the actual physical explanation of that is not that trivial.

For instance, why does the axis of the rotation not change with respect to the orbital plane? I think this is a result of some gyroscopic effect, but I am not sure.

Take the Moon, for example. It is phase-locked with the Earth -- we never see "the dark side" (it is not really always dark, of course). Why does not the same thing happen with the Earth with respect to the sun?

Tidal locking is a consequence of distance, the bodies' masses, and time. Although the moon is much smaller than the sun, its closer proximity means it exerts a greater tidal influence overall (about 2.5x greater, as far as I remember), so the moon has been locked to the earth first.

Regards,
MDL

Click to expand...

Mr.DL explained it well.

you've got a kinda intermediary example with mercury, which is not tidally locked with the sun, but has instead a 3:2 spin-orbit resonance with the sun (rotates 3 times around its axis while making 2 revolutions around the sun... the mercurial day being longer than the mercurial year).

another interesting example is pluto-charon which are always "face-to-face" (both tidally locked to each other).

but i'm afraid that might be a bit too much of information in a short time for the OP...

The axial tilt of the Earth is fixed at around 23 degrees and has a far greater contribution to the seasons than does the variation in the Earth's orbit around the Sun.

Click to expand...

another funny thing in the flat earth stuff is what they say about satellites:

"Despite the fact that in October 1957 the Soviet Union launched Sputnik, the world's first artificial satellite, Shenton proved a popular speaker to small groups, enjoying particularly talking to children, never declining an invitation. He claimed that satellites simply circled over a flat disc-world: "Would sailing round the Isle of Wight prove that it were spherical?", he demanded."

actually it does change a bit... you've got 2 variations:
- precession (rotation of the earth's rotation axis around another axis, perpendicular to the ecliptic plane, with a period of ~26000 years)
- nutation (short-term 'oscillations' of the earth's rotation axis, the largest component having a period of ~18.6 years)

Click to expand...

But the Poster wanted to know why the tilt does not change. Precession does not change it relative to orbit (? almost flunked physics) and nutation, only minutely. To change the earth's tilt will require the same thing that created it:

When that happens, we will cease worrying about Nadal's knees, Federer's reflexes, Djokovic's grin, and the location of Murray's watch.

This is a fine explanation but misses one key point -- that the tilt of the rotation axis to the plane of the Earth orbit does not change as Earth goes around the sun. In any case, while not too complicated, I doubt most people would be able to produce this explanation right away.

Tio Toni: " Rafa, your 6 month silent ban is almost up, no? You have to get your tennis racquet out and start hitting this ball again, no? We are down to our last 10 million dollars, no?!"

Rafa: " Please don't make me Tio. I no like those yellow balls anymore. I prefer those little white ones you can hit with long stick that go up and down hills and land in little hole with flag. I can make us more money if I can do that instead, no?"

you've got a kinda intermediary example with mercury, which is not tidally locked with the sun, but has instead a 3:2 spin-orbit resonance with the sun (rotates 3 times around its axis while making 2 revolutions around the sun... the mercurial day being longer than the mercurial year).

another interesting example is pluto-charon which are always "face-to-face" (both tidally locked to each other).

but i'm afraid that might be a bit too much of information in a short time for the OP...

another funny thing in the flat earth stuff is what they say about satellites: